1. Field of the Invention
The present invention relates to a water-soluble block copolymer which has a molecular chain comprising a cationic block capable of forming an ion complex with an anionic compound and a non-ionic block, and which is useful in a wide range of applications such as gene carriers, dyes and pigments dispersants for paints and inks, and the like, and the present invention relates to a manufacturing method therefor.
2. Description of the Related Art
Conventionally, poly(ethylene imine) has been used in paper manufacturing, cosmetics, water purification, and so on. However, in recent years, poly(ethylene imine), which is a cationic polymer, has been gaining attention as a gene carrier because it forms an ion complex with anionic biopolymers, such as DNA, due to an electrostatic interaction.
Poly(ethylene imine) is a conventional cationic water-soluble polymer, but when it forms an ion complex with anionic biopolymers such as DNA, it becomes insoluble in water, and as a result, the applications therefor are extremely limited.
For this reason, double-hydrophilic block copolymers have been proposed. These double-hydrophilic block copolymers have water solubility in both blocks, but both blocks have respectively different properties. As a result, a nano-micelle in which the ion complex forms a core and the non-ionic block forms a corona is formed, and the nano-micelle uniformly disperses in water. A nano-micelle obtained in this way can be used in a wide variety of applications and, in particular, is useful as a DNA carrier.
For example, a water-soluble block copolymer can be mentioned which is obtained by coupling poly(ethylene imine) with poly(ethylene glycol) having an epoxy group at one end of the molecular chain (for example, refer to Milos Sedlak, et al, “Macromolecular Chemistry and Physics”, 1999, Vol. 199, p. 247 to 254). This water-soluble block copolymer has the problem that it has poor compatibility with organic.
In addition, a random copolymer of ethyleneimine and ethyloxazoline which is obtained by hydrolysis of a part of the poly(ethyloxazoline) is also known (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2002-194116). With regard to this copolymer, since it is prepared as simply as hydrolyzing the polyethyloxazoline, even though it is a random copolymer, it is definitely not a block copolymer. Even though this random copolymer has the characteristic of forming an ionic bond with anionic compounds, it does not display the characteristic of forming an ion complex nano-micelle having a clear core and corona division as is displayed by block copolymers.
Furthermore, a graft copolymer obtained by reacting a linear poly(ethylene imine) and 2-ethyl-2-oxazoline has also been proposed (refer to Japanese Unexamined Patent Application, First Publication No. Hei 8-120035). This copolymer is a graft copolymer in which since the main chain polymer is poly(ethylene imine), the poly(2-ethyl-2-oxazoline) is bonded to the numerous nitrogen atoms within the molecule, and this is not a so-called block copolymer.